It has become more and more common that a terminal (UE/MS) can get access via a number of different access technologies. For example, mobile phones often come equipped with both cellular and WLAN (Wireless LAN) access capabilities. Laptops often have Ethernet, WLAN and sometimes also cellular access capabilities. Typically these different interfaces are used one at a time. And more importantly, a given service or a given IP session is only using one access at a time.
Currently, 3GPP EPS—Evolved Packet System (also known as 3GPP SAE—System Architecture Evolution) defines solutions for how session continuity can be achieved when a UE moves between different accesses. This can e.g. mean that a service that is running over a cellular access is moved to run over a WLAN access instead. But also with this solution, the UE is only using one access at a time and during an access change, the whole IP session and all running services within that IP session is moved from source access to target access. Simultaneous use of multiple accesses (a.k.a. multihoming) is not supported, except for very short times during a handover between two accesses.
There is work ongoing in IETF (Internet Engineering Task Force), and related work is started up in 3GPP, for defining mobility solutions in multihoming scenarios. As part of this work the concept of “flow mobility” is investigated, i.e. only a subset of the IP flows for a given IP session is moved from one access to another. For example, it could be that only the video component of a multimedia call is moved from a cellular access to WLAN, while the IP flows related to the voice component of the same call stays in the cellular access.
Policy and Charging Control (PCC) architecture was introduced in 3GPP Rel-7 and has been further evolved in 3GPP Rel-8, see FIG. 1. It provides operators with advanced tools for service-aware QoS (Quality of Service) and charging control. A PCEF (Policy and Charging Enforcement Function) is encompassed in a GW (Gateway), i.e. GGSN (Gateway GPRS Support Node) for GPRS (General Packet Radio Service) based core network and a PDN-GW (Packet Data Network Gateway) for EPC (Evolved Packet Core) based core network. When GTP (GPRS Transfer Protocol) is used to connect to the PCEF, the PCEF has bearer binding and QoS reservation capabilities. This architecture variant is referred to as on-path PCC.
The amendments in Rel-8 include support for Mobile IP based protocols in the EPC. When mobile IP is used between the GW and the Serving GW (for 3GPP based access) or in the Access GW (for non-3GPP based access), the PCC architecture must also rely on a BBERF (Bearer Binding and Event Reporting Function) for bearer binding and event reporting. The BBERF is encompassed in the Serving GW for 3GPP based access and in the Access GW for non-3GPP based access. This architecture variant is referred to as off-path PCC. In the off-path architecture the PCEF do not have the capabilities to reserve resources or to do bearer binding. A PCRF (Policy and Charging Rules Function) authorize the use of a service by installing and removing PCC rules into the PCEF and QoS rules into the BBERF (if applicable).
FIG. 1 also shows a SGSN (Serving GPRS Support Node and an MME (Mobility Management Entity). It also shows a number of reference points (Sp, Rx, Gxc, S5, Gxa, S2a, Gz, Gy, Gx, SGi) for the communication between the nodes. These nodes and reference points and part of 3GPP or non-3GPP and will not be described more in detail in this patent application.
A PCC or QoS rule defines a set of filters used to classify packets to a service data flow and an associated resource, i.e. a QoS class and a bitrate. For on-path PCC, the installation or removal of a PCC rule in the PCEF may trigger a resource request in the applicable access. For off-path PCC, the installation or removal of a QoS rule in the BBERF may trigger a resource request in the applicable access. PCC rules are installed and removed in the PCEF also in the case of off-path PCC however for this case they can not trigger a resource request in the access but they are only used for access control and charging.
Some services e.g. telephony or audio/video streaming require resources to be reserved in the target access in order to be able to provide a good enough quality of service level to the end user(s). The functionality to admit or deny the addition of any such service in the network is based on current network load. Admission control takes place at various points in the network at session setup and during handovers. For the case when dynamic PCC is deployed it is the installation of PCC or QoS rules (if applicable) with a GBR-component in the PCEF or BBERF (if applicable) that triggers this reservation of resources in the network. If the reservation of resources fails (not enough capacity in the system at some level) then the PCEF or BBERF will report this back to the PCRF and the associated service will not be admitted (for new service requests) or discontinued (handover).
Many operators today already have parallel cellular access technologies deployed such as GSM and UMTS. One lesson learned from the 1G to 2G and 2G to 3G migration is that customers are often reluctant to using the new access since coverage and capacity is not good enough in the new networks. As a consequence operators are forced to rollout their networks in a very aggressively pace in order to prevent an unacceptable call blocking rate in the new access. This is of course very expensive to the operators and even worse it creates a threshold for when a new access network may be commercially launched. A serious consequence of this is that it delays the time before the network will start to generate revenue for the operator.